1. Field of the Invention
The present invention relates to a lens barrel for use in a camera or the like.
2. Description of the Prior Art
In a conventional lens barrel, two component barrels that need to be moved together along the optical axis and rotated individually about the optical axis are typically coupled together by a bayonet coupling. In a bayonet coupling in which inclination of one component barrel with respect to the other is prevented by a flange portion having a carefully determined diameter, the bayonet pins that are formed on one component barrel are introduced into the bayonet slots formed in the other component barrel through clearance slots formed in the flange portion, which is formed around the latter component barrel. Here, the bayonet pins need to be introduced in such a way that, in normal use, they do not move out of the bayonet slots, i.e. outward beyond the flange portion.
However, to prevent inclination of one component barrel with respect to the other, it is usual to arrange three of such bayonet pins of an identical shape, for example, at 120.degree. intervals about the optical axis. As a result, when one component barrel rotates through 120.degree. with respect to the other, all or part of the bayonet pins may move out of the bayonet slots, i.e. beyond the flange portion, through the clearance slots, causing disengagement or inclination of one component barrel from or with respect to the other. On the other hand, reducing the number of bayonet pins in an attempt to obtain as large a rotation angle as possible makes it difficult to prevent inclination between the component barrels.
For these reasons, in some conventional lens barrels, in particular where a large rotation angle is desired, two component barrels that need to be moved together along the optical axis and rotated individually about the optical axis are coupled together by the use of an additional component provided separately from those two component barrels, as in a zoom lens barrel of the type in which a lens is driven by the use of a stepped cam, i.e. a cam that has separate cam portions for zooming and for focusing. This, however, leads to an undesirable increase in the size and the production cost of the zoom lens barrel.